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Are you saying that you have a Varitrane VAV box with a direct coupled actuator? If so than it will normally be a typical 5/8 shaft and most brands will be compatible. You will need to make sure that it is a floating type control, Power to open and power to close.
The problem though will be in the connection to the UCM board which requires a wire harness. If you have an existing air valve actuator than you can simply reuse it. If not I would suggest buying OEM from Trane which make a direct coupled actuator along with harness installed.

Yes, it is a VAV but it is not what I would call direct coupled, it is a OLD system and has the board and actuator (small clock motor and some reduction gears) all in one assembly. I am replacing with Alerton and hopefully a Honeywell ML6161 actuator I am going to attemp to attach a couple of pictures, one is of the board and the other is from below looking at the drive gears and end switches behind the board. My concern is that the main drive gear hub is giving me a indication that the actual damper shaft may be a 1/4" or less. If the pictures attach, on a side note, I am sure that the lower left terminals are comm, the upper right, power? Lower right???? Thank you for your response alcomech.

I get it, that's old timing stuff your playing with, early 90's maybe?
So are you going to take out the entire assembly including the UCM control and replace with a new controller. You then will be able to install a direct couple actuator such as the ML6161B2024, you may have to get a shaft extension and will use a reducing bushing to connect to the shaft.

You may want to consider installing a new complete low leakage damper along with static or velocity controller. Hope this helps

That would be nice but you know salesmen, "was not in my quote", as I found out yesterday, even the motors are not in the quote. We are going to remove the controller and replace with Alerton and then reuse the existing clock motor "actuator" if it still works. Do you know what the wire colors are for the motor off the top of your head? It looks like red and blue going to the board, I assume clockwise and counter clockwise and common somewhere behind? Thanks for the help.